Method of preserving wood and solutions therefor



Patented Feb. 14, 1928.

UNITED STATES LEO r, comm, or

PATENT OFFICE.

FREEHOIJJ, NEW JERSEY, ASSIGNOR TO CUBTIN-HOWE-OORPORA- TION, A COB-PORTION OF YORK.

I LIETEOD OF PB'BSEBVING WOOD AND SOLUTIONS TB.

K Drawing.

In my eopending application, Serial. No. 39,391 filed June 24, 1925, Lhave disclosed and claimed a method of protecting vegetable substances from attack b insects, fungi,

etc., and specifically a metho for preserving wood, comprising treating the vegetable substance, or impregnating the wood, with an aqueous solution containing water-soluble components capable of reacting, on exposure to the atmosphere, to deposit a body of low solubility and hi h toxicity, the reaction being characterize by a progressive'increase in the basicity of the solution. A typical 3 example of this method as disclosed in the i said application, involves dissol cupric acetate and arsenous acid in equimo ar proportions in water, preparing solutions of the order of 1% to 5% concentration with respect to the copper salt. This solution loses acetic acid upon exposure to the air,

becoming progressively more basic and precipitating an aceto-arsenite of copper.- Y My further researches have shown that zinc meta-arsenite may be precipitated in similar manner in situ within the body of the wood; and that the precipitate so formed is a big}:- ly eflicient preservative for the wood. e

use of zinc in this proces presents certain advantages over that of cofpper: notably in that zinc acetate has been ound to be practlcally non-corrosive toward iron, so that the impregnation may be carried out either in open tanks or pressure vmels as may be desired. Gupric acetate on the contrary strongly attacks iron and steel.

The reaction involved may conveniently be assumed to be as follows:

the zinc meta-arsenite depositing in solid phase as the original clear solution becomes progressively more basic owing to the loss of acetic acid by volatilization.

Analyses of the. recipitate have indicated that it is in all pro ability largely at least a zinc salt of meta-arsenous acid, HAsO,.- Inasmuch as meta-arsenous acid is slightly stronger than ortho-arsenous acid, it was regarded as possible that its salts might prove to have low toxic value for the reason that the might not be dissolved bythe weak acids arising out of the vital processes of the wood-rotting fungi. Direct t has ing prepared Application fled Iay 15, 1926. Serial No. 109,436.

however shown that this is not the case, and that zinc meta-arsenite is a stron toxic agent for these fungi, having approximately higher toxicity than the ortho-arsenite and hence an excellent preservative for wood.

The salt is preferably applied in the form of a solution of about one to two percent concentration or less, a typical solution be by dissolving in98 parts by weight of water:

Parts. Z1110 chlond ZnCl 0.972 Calcium acetate Ca(CH,COO) H 0. 1206 Arsenlc A5 0 1.4.00 Acetic acid .100

Zinc sulfate may be substituted for zinc chlorid. In formulae-containing both calcium-ion and sulfate-ion, the treating solution is first separated by decantation or filtration from any precipitate of calcium sulfate WhlCh may form. The function of the small amount of acetic acid is to prevent the light precipitation of toxic material which might occur prematurely in its absence, and-to insure the precipitation of the meta-arsenite.

As heretofore stated, my invention is not to the use of the s filutions foil;e wood impregnation purposes. ey may employed for example for all insecticidal or flmgicidal purposes, for which they posses certain advantages as compared with the usual aqueous suspensions of toxic compounds. These suspensions deposit toxic compounds over an area which is in general, less than the total area wetted by the liquid by which they. are carried. My solutions on the contrary, when spread'in the form of thin films upon foliage, undergo a relativel rapid decomposition or chemical change e result of containing jwater-soluble components capas ble of reacting, on exposure to the atmosphere, to deposit zinc'meta-arsenite within the bodylof-tt hewoodn 2. Method" of protecting vegetable substancesfrom attack by insects, fungi, etc, comprisingapplying thereto an aqueoussolution containin water-soluble components capable of reacting, on exposure to the atmosphere, andrwithpprogressive increase in basicity, to deposit. a zinc-arsenic compound. of low solubility and high toxicity 3; Method of preserving wood-comprising "impregnating" it with an aqueous solution scontainiiig water so'luble components capa- -'e1'!' po'sureto'the atmosbleo'fng, o phelr e,'**an'd' "with; progressive increase in -bas'i'city, t' deph's'it within the a body of the "wood a zinc-arsenic compound of low solua'hd ox i c'itybi I I Methtidofpreserving wood comprising impregn in it, with t 'anil,iaqueous' solution Containing water-soluble components *c'apa, ble of reacting, on exposure theatmos-' pher'e,} and with progressi increase in basicity, the deposit zinc meta-arsenite within the body of the wood.

5. An insecticidal and fungicidalsolution comprising water-soluble components capable of reacting, on suflicient exposure to the atmosphere, to deposit zinc meta-arsenite.

6. An insecticidal and fungicidal solution comprising water-soluble components, including compounds of zinc and arsenic, ca-' pable of reacting on suflicient exposure to the atmosphere, and with progressive increase in basicity, to deposit a toxic zincarsenic compound of low solubility, said solution'sufliciently stable to permit impregnation of wood therewith. 3

7. An insecticidal and fungicidal solution comprising water-soluble components cape-- ble of reacting, on sufiici'ent exposure to the atmosphere, and with progressive increase in basicity, to deposit zinc metaarsenite. 8. An article of wood impregnated with zinc meta-arsenite;

In testimony whereof, I atfix my signa-' ture- LEO P. CUBTIN. 

